The present invention relates generally to optical lens systems and more particularly to a wide angle telecentric lens assembly adapted to project an enlarged image of an object onto an image plane.
The prior art is replete with various projection lens assemblies for use in specific applications. In general, however, these lens assemblies do not have long back focal distances as compared with the overall equivalent focal length of the lens assembly. Moreover, such lens assemblies do not incorporate a telecentric entrance pupil (i.e., where the chief rays of the light beams entering the lens assembly are parallel). There are, however, certain projection applications, wherein a telecentric entrance pupil is required along with a beam splitting prism and/or similar optical elements positioned directly in front of the object, such as in a liquid crystal light valve projection system which includes a Xenon arc lamp projected into a refracting prism in a direction perpendicular to the optical axis for reflection back towards the object plane where it optically interacts with the light valve and a cathode ray tube to be reflected forward through the prism towards the image plane. Therefore, a lens assembly having a long back focal distance relative to the equivalent focal length of the lens assembly is required.
However, telecentric lens designs characteristically exhibit certain particular residual aberrations. These include pincushion distortion (as viewed on the projection screen), coma, field curvature, astignatism, secondary lateral chromatic aberration and spherical aberration of the chief rays. Thus, the lens system must be capable of bringing all of these aberrations into an overall state of balance, resulting in a sharp, pleasing image over the entire field of view. In addition, as a matter of general lens design, such balance should be achieved with a minimum number of component lens elements.
Accordingly, it is an object of the present invention to provide a new and improved projection lens system. Another object of the invention is to provide a new and improved wide angle projection lens system.
It is also an object of the present invention to provide a new and improved wide angle projection lens system having a telecentric entrance pupil with a relatively long back focal distance.
It is an additional object of the present invention to provide a new and improved wide angle projection lens system having a telecentric entrance pupil and a relatively long back focal distance yet requires relatively few lens elements to provide nearly diffraction-limited imaging.
It is yet another object of the present invention to provide a new and improved wide-angle projection lens system having a telecentric entrance pupil and a relatively long back focal distance, which provides nearly diffraction limited imaging despite the presence of beam splitting and/or other optical elements between the object and the lens assembly.
It is still another object of the present invention to provide a new and improved wide angle projection lens system having a telecentric entrance pupil and a relatively long back focal distance, yet a finite F-number, which permits nearly diffraction-limited imaging despite the presence of beam splitting and/or other optical elements between the object and the lens assembly.
It is a further object of the present invention to provide a new and improved wide angle projection lens system having a telecentric entrance pupil and a relatively long back focal distance, which provides nearly diffraction-limited imaging with relatively good edge light illumination, despite the presence of beam splitting and/or other optical elements between the object and the lens assembly.
Objects and advantages of the present invention have been set forth in part above and in part below, or may be appreciated from the description herein or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims. Accordingly, the invention resides in the novel parts, structures, arrangements, combinations, and improvements herein shown and described.